Is it possible to have a narcolepsy diagnosis in a patient who never had rem sleep during an mslt's naps?

Maybe: The international classification of sleep disorders has specific criteria which must be met to diagnose someone with narcolepsy. As part of these criteria, you need to have 2 or more episodes of sleep onset-rems during the mslt. However, if the spinal fluid level of hypocretin is low, you can also make the diagnosis. But, you can have excessive daytime sleepiness that is not narcolepsy.

Yes: Other reasons may occur for no rem. If person with cataplexy they do not need this test for absolute diagnosis. If patient on medications that suppress rem that could be another cause.